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| United States Patent |
5,532,119
|
|
Arcus
, et al.
|
July 2, 1996
|
High-speed direct-positive photographic elements utilizing core-shell
emulsions
Abstract
Direct-positive photographic elements are comprised of a support and a
silver halide emulsion layer containing core-shell silver halide grains
comprising a chemically sensitized core and a chemically sensitized shell,
wherein at least one of the core and the shell comprises a band of dopant
and wherein the dopant is hexacyano ruthenium (II). Preferably, the shell
of the core-shell grains is chemically sensitized with both a
gold-containing chemical sensitizing agent and a sulfur-containing
chemical sensitizing agent and the weight ratio of the gold-containing
chemical sensitizing agent to the sulfur-containing chemical sensitizing
agent is at least about two to one.
| Inventors:
|
Arcus; Robert A. (Penfield, NY);
Marchetti; Alfred P. (Penfield, NY)
|
| Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
| Appl. No.:
|
037066 |
| Filed:
|
March 25, 1993 |
| Current U.S. Class: |
430/567; 430/598; 430/603; 430/604; 430/605 |
| Intern'l Class: |
G03C 001/035 |
| Field of Search: |
430/567,598,603,604,605
|
References Cited
U.S. Patent Documents
| 3672901 | Mar., 1970 | Ohkubo et al. | 430/569.
|
| 4395478 | Jul., 1983 | Hoyen | 430/605.
|
| 4617258 | Oct., 1986 | Menjo et al. | 430/605.
|
| 4643965 | Feb., 1987 | Kubota et al. | 430/567.
|
| 4806462 | Feb., 1989 | Yamashita et al. | 430/604.
|
| 4863845 | Sep., 1989 | Murai et al. | 430/605.
|
| 4937180 | Jun., 1990 | Marchetti et al. | 430/567.
|
| 4945035 | Jul., 1990 | Keevert et al. | 430/567.
|
| 4981780 | Jan., 1991 | Inoue et al. | 430/598.
|
| 4996137 | Feb., 1991 | Inoue et al. | 430/598.
|
| 5030553 | Jul., 1991 | Kuwashima et al. | 430/598.
|
| 5112732 | May., 1992 | Hayashi et al. | 430/604.
|
| Foreign Patent Documents |
| 0573066 | Dec., 1993 | EP.
| |
Other References
United States Statutory Invention Registration H1294 to Tamada et al., Mar.
1, 1994.
|
Primary Examiner: Baxter; Janet C.
Attorney, Agent or Firm: Lorenzo; Alfred P.
Claims
What is claimed is:
1. A direct-positive photographic element comprising a support and a silver
halide emulsion layer containing core-shell silver halide grains
comprising a chemically sensitized core and a chemically sensitized shell,
at least one of said core and said shell comprising a band of dopant,
characterized in that said dopant is hexacyano ruthenium (II).
2. A direct-positive photographic element as claimed in claim 1, wherein
said hexacyano ruthenium (II) is present only in said core.
3. A direct-positive photographic element as claimed in claim 1, wherein
said hexacyano ruthenium (II) is present only in said shell.
4. A direct-positive photographic element as claimed in claim 1, wherein
said hexacyano ruthenium (II) is present in both said core and said shell.
5. A direct-positive photographic element as claimed in claim 1, wherein
said hexacyano ruthenium (II) is present in said core-shell silver halide
grains in an amount of from about 10 to about 1000 parts per million by
weight based on the weight of silver in said core-shell silver halide
grains.
6. A direct-positive photographic element as claimed in claim 1, wherein
said hexacyano ruthenium (II) is present in said core-shell silver halide
grains in an amount of from about 25 to about 400 parts per million by
weight based on the weight of silver in said core-shell silver halide
grains.
7. A direct-positive photographic element as claimed in claim 1, wherein
said hexacyano ruthenium (II) is present in said core-shell silver halide
grains in an amount of from about 50 to about 200 parts per million by
weight based on the weight of silver in said core-shell silver halide
grains.
8. A direct-positive photographic element as claimed in claim 1, wherein
said core is chemically sensitized with both a gold-containing chemical
sensitizing agent and a sulfur-containing chemical sensitizing agent.
9. A direct-positive photographic element as claimed in claim 1, wherein
said shell is chemically sensitized with both a gold-containing chemical
sensitizing agent and a sulfur-containing chemical sensitizing agent.
10. A direct-positive photographic element as claimed in claim 1, wherein
both said core and said shell are chemically sensitized with both a
gold-containing chemical sensitizing agent and a sulfur-containing
chemical sensitizing agent.
11. A direct-positive photographic element as claimed in claim 1, wherein
said shell is chemically sensitized with both a gold-containing chemical
sensitizing agent and a sulfur-containing chemical sensitizing agent and
the weight ratio of said gold-containing chemical sensitizing agent to
said sulfur-containing chemical sensitizing agent is at least about 2 to
1.
12. A direct-positive photographic element as claimed in claim 1, wherein
said shell is chemically sensitized with a combination of potassium
chloroaurate and sodium thiosulfate.
13. A direct-positive photographic element as claimed in claim 1, wherein
said element is spectrally sensitized with a cyanine or merocyanine
spectral sensitizing dye.
14. A direct-positive photographic element as claimed in claim 1, wherein
said core-shell silver halide grains have a mean grain size in the range
of from about 0.1 to about 0.6 micrometers.
15. A direct-positive photographic element as claimed in claim 1, wherein
said core-shell silver halide grains have a mean grain size in the range
of from about 0.2 to about 0.5 micrometers.
16. A direct-positive photographic element as claimed in claim 1, wherein
said silver halide emulsion layer comprises an aromatic hydrazide
nucleating agent.
17. A direct-positive photographic element as claimed in claim 1, wherein
said silver halide emulsion layer comprises, as a nucleating agent, an
N-substituted cycloammonium quaternary salt.
18. A direct-positive photographic element as claimed in claim 1, wherein
said silver halide emulsion layer comprises a nucleating agent of the
formula:
##STR4##
wherein z represents the atoms completing a heterocyclic quaternary
ammonium nucleus comprised of an azolium or azinium ring;
R.sup.1 is hydrogen or methyl;
R.sup.2 is hydrogen or an alkyl substituent of from 1 to 8 carbon atoms;
R.sup.3 is hydrogen or a substituent having a Hammett sigma value derived
electron withdrawing characteristic more positive than -0.2;
X is a charge balancing counter ion; and
n is 0 or 1; and
Z or R.sup.3 includes a thioamido adsorption promoting moiety.
19. A direct-positive photographic element as claimed in claim 1, wherein
said silver halide emulsion layer comprises a nucleating agent of the
formula:
##STR5##
Description
FIELD OF THE INVENTION
This invention relates in general to photography and in particular to
direct-positive photographic elements. More specifically, this invention
relates to high-speed direct-positive photographic elements containing
doped core-shell silver halide grains.
BACKGROUND OF THE INVENTION
Photographic elements which produce images having an optical density
directly related to the radiation received on exposure are said to be
negative-working. A positive photographic image can be formed by producing
a negative photographic image and then forming a second photographic image
which is a negative of the first negative--that is, a positive image. A
direct-positive image is understood in photography to be a positive image
that is formed without first forming a negative image. Direct-positive
photography is advantageous in providing a more straight-forward approach
to obtaining positive photographic images.
A conventional approach to forming direct--positive images is to use
photographic elements employing internal latent image-forming silver
halide grains. After imagewise exposure, the silver halide grains are
developed with a surface developer--that is, one which will leave the
latent image sites within the silver halide grains substantially
unrevealed. Simultaneously, either by uniform light exposure or by the use
of a nucleating agent, the silver halide grains are subjected to
development conditions that would cause fogging of a negative-working
photographic element. The internal latent image-forming silver halide
grains which received actinic radiation during imagewise exposure develop
under these conditions at a slow rate as compared to the internal latent
image-forming silver halide grains not imagewise exposed. The result is a
direct-positive silver image. In color photography, the oxidized developer
that is produced during silver development is used to produce a
corresponding direct-positive dye image. Multi-color direct-positive
photographic images have been extensively investigated in connection with
image transfer photography.
Direct-positive internal latent image-forming emulsions can take the form
of halide-conversion type emulsions. Such emulsions are illustrated by
Knott et al U.S. Pat. No. 2,456,943 and Davey et al U.S. Pat. No.
2,592,250.
More recently the art has found it advantageous to employ core-shell
emulsions as direct-positive internal latent image-forming emulsions. An
early teaching of core-shell emulsions is provided by Porter et al U.S.
Pat. No. 3,206,313, wherein a coarse grain monodispersed chemically
sensitized emulsion is blended with a finer grain emulsion. The blended
finer grains are Ostwald ripened onto the chemically sensitized larger
grains. A shell is thereby formed around the coarse grains. The chemical
sensitization of the coarse grains is "buried" by the shell within the
resulting core-shell grains. Upon imagewise exposure, latent image sites
are formed at internal sensitization sites and are therefore also
internally located. The primary function of the shell structure is to
prevent access of the surface developer to the internal latent image
sites, thereby permitting low minimum densities.
The chemical sensitization of the core emulsion can take a variety of
forms. One technique is to sensitize the core emulsion chemically at its
surface with conventional sensitizers, such as sulfur and gold. Atwell et
al U.S. Pat. No. 4,035,185 teaches that controlling the ratio of middle
chalcogen to noble metal sensitizers employed for core sensitization can
control the contrast produced by the core-shell emulsion. Another
technique that can be employed is to incorporate a metal dopant, such as
iridium, bismuth, or lead, in the core grains as they are formed.
The shell of the core-shell grains need not be formed by Ostwald ripening,
as taught by Porter et al, but can be formed alternatively by direct
precipitation onto the sensitized core grains. Evans U.S. Pat. Nos.
3,761,276, 3,850,637, and 3,923,513 teach that further increases in
photographic speed can be realized if, after the core-shell grains are
formed, they are surface chemically sensitized. Surface chemical
sensitization is, however, limited to maintain a balance of surface and
internal sensitivity favoring the formation of internal latent image
sites.
Direct-positive emulsions exhibit art-recognized disadvantages as compared
to negative-working emulsions. Although Evans, cited above, has been able
to increase photographic speeds by properly balancing internal and surface
sensitivities, direct-positive emulsions have not achieved photographic
speeds equal to the faster surface latent image forming emulsions. Second,
direct-positive core-shell emulsions are limited in their permissible
exposure latitude. When exposure is extended, rereversal occurs. That is,
in areas receiving extended exposure a negative image is produced. This is
a significant limitation to in-camera use of direct-positive photographic
elements, since candid photography does not always permit control of
exposure conditions. For example, a very high contrast scene can lead to
rereversal in some image areas.
Radiation-sensitive emulsions which are comprised of core-shell silver
halide grains and are adapted to form direct-positive images are also
described in detail in T. H. James, "The Theory Of The Photographic
Process", Fourth Edition, Chapter 7, pages 182 to 193, MacMillan
Publishing Co., (1977).
Incorporation in the aforesaid core-shell silver halide grains of certain
polyvalent metal ions for the purpose of reducing rereversal is described
in Hoyen, U.S. Pat. No. 4,395,478, issued Jul. 26, 1983. In particular,
Hoyen discloses incorporation in the shell portion of such grains of one
or more polyvalent metal ions chosen from the group consisting of
manganese, copper, zinc, cadmium, lead, bismuth and lanthanides. While the
use of such doping agents represents a major advance in the art by
minimizing the rereversal problem, the direct-positive photographic
elements described by Hoyen do not exhibit as high a level of photographic
speed as is needed to satisfy current requirements, especially when the
direct-positive elements are used in COM (computer output microfilm)
applications.
It is toward the obective of providing improved direct-positive
photographic elements with markedly enhanced speed characteristics that
the present invention is directed.
SUMMARY OF THE INVENTION
In accordance with this invention, novel direct-positive photographic
elements are comprised of a support and a silver halide emulsion layer
containing core-shell silver halide grains comprising a chemically
sensitized core and a chemically sensitized shell, at least one of the
core and the shell comprising a band of dopant, characterized in that the
dopant is hexacyano ruthenium (II).
The improved direct-positive photographic elements of this invention
provide excellent photographic speed together with the many advantages and
conveniences of a direct-positive system. While similar high speeds can be
obtained by use of negative-working elements that provide reversal images
via an additional dichromate bleach and a second development step in
processing, the use of dichromate bleaches and additional processing
solutions is undesirable from both cost and environmental standpoints. By
use of the invention described herein, silver halide grain size can be
kept small enough that the quality of microfilm images is not compromised
yet the desired high speed can nonetheless be achieved. Attempts to obtain
the desired high speed by use of relatively large size silver halide
grains are not feasible since the resulting high degree of granularity is
unacceptable for microfilm images.
In carrying out this invention, hexacyano ruthenium (II) is incorporated
into either the core or the shell or both during precipitation of the
silver halide grains by incorporating into the reactant mixture a suitable
salt of hexacyano ruthenium (II), for example an alkali metal salt such as
sodium hexacyano ruthenium (II) which has the formula Na.sub.4
Ru(CN).sub.6 or potassium hexacyano ruthenium (II) which has the formula
K.sub.4 Ru(CN).sub.6.
The use of hexacyano ruthenium (II) as a doping agent in silver bromide
emulsions to provide increased stability, both in terms of observed speed
and minimum density, and to provide reductions in low intensity
reciprocity failure is described in Marchetti et al, U.S. Pat. No.
4,937,180, issued Jun. 26, 1990. The use of hexacyano ruthenium (II) as a
doping agent in silver chloride emulsions to provide increased sensitivity
is described in Keevert et al, U.S. Pat. 4,945,035, issued Jul. 31, 1990.
However, both of these patents relate to the use of doping agents in
negative-working emulsions, whereas the present invention pertains to
direct-positive core-shell emulsions and these function by distinctly
different mechanisms.
As described in the aforesaid U.S. Pat. Nos. 4,937,180 and 4,945,035, it is
believed that the entire metal complex is incorporated intact into the
silver halide grains. Thus, both the ruthenium and the cyano ligands
function together in this invention to provide doping which enhances
photographic speed in a direct-positive system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The doping agent utilized in this invention, namely hexacyano ruthenium
(II), is typically employed in an amount of from about 10 to about 1000
ppm (parts per million) by weight based on the weight of silver in the
silver halide grains. Preferred amounts are in the range of from about 25
to about 400 ppm; while particularly preferred amounts are in the range of
from about 50 to about 200 ppm. The hexacyano ruthenium (II) can be
present in either the core or the shell of the core-shell grains or in
both the core and the shell.
The formation of core-shell emulsions according to the present invention
can begin with any convenient conventional sensitized core emulsion. The
core emulsion can be comprised of silver bromide, silver chloride, silver
chlorobromide, silver chloroiodide, silver bromoiodide, or silver
chlorobromoiodide grains. The grains can be coarse, medium, or fine and
can be bounded by any crystal planes, such as 100, 111 or 110. Prior to
shelling, the core grains are preferably monodisperse. That is, the core
grains prior to shelling preferably exhibit a coefficient of variation of
less than 20% and for very high contrast applications optimally exhibit a
coefficient of variation of less than 10%. The preferred completed
core-shell emulsions of this invention exhibit similar coefficients of
variation. (As employed herein the coefficient of variation is defined as
100 times the standard deviation of the grain diameter divided by the
average grain diameter.) Although other sensitizations of the core
emulsions are possible and contemplated, it is preferred to surface
chemically sensitize the core emulsion grains with a combination of middle
chalcogen and noble metal sensitizers, as taught by Atwell et al, cited
above. Additionally either middle chalcogen or noble metal sensitization
can be employed alone. Sulfur, selenium, and gold are preferred
sensitizers.
Although the sensitized core emulsion can be shelled by the Ostwald
ripening technique of Porter et al, cited above, it is preferred that the
silver halide forming the shell portion of the grains be precipitated
directly onto the sensitized core grains by the double-jet addition
technique. Double-jet precipitation is well known in the art as
illustrated by Research Disclosure,Vol. 176, December 1978, Item 17643,
Section I, here incorporated by reference. Research Disclosure and its
predecessor, Product Licensing Index, are publications of Industrial
Opportunities Ltd., Homewell, Havant, Hampshire, P09 1EF, United Kingdom.
The halide content of the shell portion of the grains can take any of the
forms described above with reference to the core emulsion. Shells with a
high content of chloride provide advantages with respect to developability
and low intensity reciprocity failure. On the other hand, the highest
realized photographic speeds are generally recognized to occur with
predominantly bromide grains, as taught by Evans, cited above. Thus, the
specific choice of a preferred halide for the shell portion of the
core-shell grains will depend upon the specific photographic application.
The silver halide forming the shell portion of the core-shell grains must
be sufficient to restrict developer access to the sensitized core portion
of the grains. This will vary as a function of the ability of the
developer to dissolve the shell portion of the grains during development.
Although shell thicknesses as low as a few cyrstal lattice planes for
developers having very low silver halide solvency are taught in the art,
it is preferred that the shell portion of the core-shell grains be present
in a molar ratio with the core portion of the grains of about 1:4 to 8:1,
as taught by Porter et al and Atwell et al. In some instances, even lower
ratios such as ratios of 1:6 or less are desirable.
After precipitation of a shell portion onto the sensitized core grains to
complete formation of the core-shell grains, the emulsions can be washed,
if desired, to remove soluble salts. Conventional washing techniques can
be employed, such as those disclosed by Research Disclosure, Item 17643,
cited above, Section II, here incorporated by reference.
In the core-shell emulsions of this invention, both the core and the shell
are chemically sensitized. To chemically sensitize the shell, any type of
surface chemical sensitization known to be useful with corresponding
surface latent image-forming silver halide emulsions can be employed, such
as disclosed by Research Disclosure, Item 17643, cited above, Section III.
Middle chalcogen and/or noble metal sensitizations, as described by Atwell
et al, cited above, are preferred. Sulfur, selenium and gold are
specifically preferred surface sensitizers.
The degree of surface chemical sensitization is limited to that which will
increase the speed of the internal latent image-forming emulsion, but
which will not compete with the internal sensitization sites. Thus, a
balance between internal and surface sensitization is preferably
maintained for maximum speed, but with the internal sensitization
predominating.
It is particularly preferred, in this invention, that the shell of the
core-shell grains is chemically sensitized with both a gold-containing
chemical sensitizing agent and a sulfur-containing chemical sensitizing
agent and that the weight ratio of the gold-containing chemical
sensitizing agent to the sulfur-containing chemical sensitizing agent be
at least about 2 to 1. Use of such weight ratios of gold sensitizer to
sulfur sensitizer has been unexpectedly found to provide increased
photographic speed with reduced granularity for a given grain size.
The use of gold compounds as chemical sensitizers is very well known in the
art (see, for example, U.S. Pat. Nos. 3,297,446 and 3,503,749). Gold
compounds that are especially useful as chemical sensitizers in this
invention include gold chloride, gold sulfide, gold iodide, potassium
chloroaurate, potassium aurothiocyanate, chloroauric acid tetrahydrate,
aurous dithiosulfate, and the like. Potassium chloroaurate is particularly
preferred.
Sodium thiosulfate, which is a very commonly used example of a
sulfur-containing chemical sensitizing agent, is preferably used in this
invention in combination with one or more of the gold-containing chemical
sensitizing agents described above.
It is preferred that the core-shell silver halide grains utilized in this
invention have a mean grain size in the range of from about 0.1 to about
0.6 micrometers, and more preferably in the range of from about 0.2 to
about 0.5 micrometers. Methods for determining the mean grain size of
silver halide grains are well known in the photographic art. They are
described, for example, in T. H. James, The Theory Of The Photographic
Process, Fourth Edition, pages 100 to 102, MacMillan Publishing Co.
(1977).
The core-shell emulsions of the present invention can, if desired, be
spectrally sensitized. For multicolor photographic applications, red,
green, or, optionally, blue spectral sensitizing dyes can be employed,
depending upon the portion of the visible spectrum the core-shell grains
are intended to record. For black-and-white imaging applications spectral
sensitizing is not required, although orthochromatic or panthromatic
sensitization is usually preferred. Generally, any spectral sensitizing
dye or dye combination known to be useful with a negative-working silver
halide emulsion can be employed with the core-shell emulsions of the
present invention. Illustrative spectral sensitizing dyes are those
disclosed in Research Disclosure, item 17643, cited above, Section IV.
Particularly preferred spectral sensitizing dyes are those disclosed in
Research Disclosure, Vol. 151, November, 1976, Item 15162, here
incorporated by reference. Although the emulsions can be spectrally
sensitized with dyes from a variety of classes, preferred spectral
sensitizing dyes are polymethine dyes, which include cyanine, merocyanine,
complex cyanine and merocyanine (i.e., tri-, tetra-, and poly-nuclear
cyanine and merocyanine), oxonol, hemioxonol, styryl, merostyryl, and
streptocyanine dyes. Cyanine and merocyanine dyes are specifically
preferred. Spectral sensitizing dyes which sensitize surface-fogged
direct-positive emulsions generally desensitize both negative-working
emulsions and the core-shell emulsions of this invention and therefore are
not normally contemplated for use in the practice of this invention.
Spectral sensitization can be undertaken at any stage of emulsion
preparation heretofore known to be useful. Most commonly, spectral
sensitization is undertaken in the art subsequent to the completion of
chemical sensitization. However, it is specifically recognized that
spectral sensitization can be undertaken alternatively concurrently with
chemical sensitization or can entirely precede chemical sensitization.
Sensitization can be enhanced by pAg adjustment including cycling, during
chemical and/or spectral sensitzation.
The core-shell emulsions of this invention preferably incorporate a
nucleating agent to promote the formation of a direct-positive image upon
processing. The nucleating agent can be incorporated in the emulsion
during processing, but is preferably incorporated in manufacture of the
photographic element, usually prior to coating. This reduces the
quantities of nucleating agent required. The quantity of nucleating agent
required can also be reduced by restricting the mobility of the nucleating
agent in the photographic element. Large organic substituents capable of
performing, at least to some extent, a ballasting function are commonly
employed. Nucleating agents which include one or more groups to promote
adsorption to the surface of the silver halide grains have been found to
be effective in extremely low concentrations.
The term "nucleating agent" is employed herein in its art-recognized usage
to mean a fogging agent capable of permitting the selective development of
internal latent image-forming silver halide grains which have not been
imagewise exposed, in preference to the development of silver halide
grains having an internal latent image formed by imagewise exposure.
Nucleating agents which are useful in this invention, including both
aromatic hydrazides and N-substituted cycloammonium quaternary salts, are
described in full detail in Hoyen, U.S. Pat. No. 4,395,478, issued Jul.
26, 1983.
Particularly preferred nucleating agents for use in this invention are
compounds of the formula:
##STR1##
wherein Z represents the atoms completing a heterocyclic quaternary
ammonium nucleus comprised of an azolium or azinium ring;
R.sup.1 is hydrogen or methyl;
R.sup.2 is hydrogen or an alkyl substituent of from 1 to 8 carbon atoms;
R.sup.3 is hydrogen or a substituent having a Hammett sigma value derived
electron withdrawing characteristic more positive than -0.2;
X is a charge balancing counter ion; and
n is 0 or 1; and
Z or R.sup.3 includes a thioamido adsorption promoting moiety.
Nucleating agents of the above formula are described in Parton et al, U.S.
Pat. No. 4,471,044, issued Sep. 11, 1984.
Once core-shell emulsions have been generated by precipitation procedures,
washed, and sensitized, as described above, their preparation can be
completed by the optional incorporation of nucleating agents, described
above, and conventional photographic addenda, and they can be usefully
applied to photographic applications requiring a silver image to be
produced--e.g., conventional black-and-white photography.
The core-shell emulsion is comprised of a dispersing medium in which the
core-shell grains are dispersed. The dispersing medium of the core-shell
emulsion layers and other layers of the photographic elements can contain
various colloids alone or in combination as vehicles (which include both
binders and peptizers). Preferred peptizers are hydrophilic colloids,
which can be employed alone or in combination with hydrophobic materials.
Preferred peptizers are gelatin--e.g., alkali-treated gelatin (cattle bone
or hide gelatin) and acid-treated gelatin (pigskin gelatin) and gelatin
derivatives--e.g., acetylated gelatin, phthalated gelatin, and the like.
Useful vehicles are illustrated by those disclosed in Research Disclosure,
Item 17643, cited above, Section IX, here incorporated by reference. The
layers of the photographic elements containing crosslinkable colloids,
particularly the gelatin-containing layers, can be hardened by various
organic and inorganic hardeners, as illustrated by Research Disclosure,
Item 17643, cited above, Section X.
Instability which decreases maximum density in direct-positive emulsion
coatings can be protected against by incorporation of stabilizers,
antifoggants, latent image stabilizers and similar addenda in the emulsion
and contiguous layers prior to coating. A variety of such addenda are
disclosed in Research Disclosure, Item 17643, cited above Section VI.
The high-speed direct-positive photographic elements of this invention can
utilize any of the support materials known for use in the photographic
arts. Typical of useful polymeric film supports are films of cellulose
nitrate and cellulose esters such as cellulose triacetate and diacetate,
polystyrene, polyamides, homo- and co-polymers of vinyl chloride,
poly(vinylacetal), polycarbonate, homo- and co-polymers of olefins, such
as polyethylene and polypropylene and polyesters of dibasic aromatic
carboxylic acids with divalent alcohols, such as poly(ethylene
terephthlate).
Polyester films, such as films of polyethylene terephthalate, have many
advantageous properties, such as excellent strength and dimensional
stability, which render them especially advantageous for use as supports
in the present invention.
The invention is further illustrated by the following examples of its
practice. In these examples, the mean grain size of the core-shell grains
is specified in micrometers, the concentration of the doping agent
hexacyano ruthenium (II) is specified in parts per million by weight based
on the weight of silver in the doped core or the doped shell, as
appropriate, and the concentration of nucleator is specified in millimoles
per mole of total silver in the core-shell grains. Values reported in the
examples for granularity are root mean square granularity values as
described in T. H. James, "The Theory Of The Photographic Process", Fourth
Edition, Page 619, MacMillan Publishing Co. (1977). Nucleating agents
utilized in the examples are nucleator N-A which has the formula:
##STR2##
and nucleator N-B which has the formula:
##STR3##
EXAMPLES 1-4
A core-shell emulsion, designated Emulsion A and employed herein as a
control, was prepared in the following manner.
Precipitation of Core
A 4.5 liter aqueous solution (designated solution G) containing 70 grams of
inert gelatin, 0.225 grams of a linear ethylene glycol surfactant and 3.7
grams of sodium bromide was adjusted to a pH of 2.0 at 20.degree. C. and
added to a reaction vessel. The temperature was raised to 70.degree. C.
and the pAg adjusted to 8.36 by dropwise addition from a 3.56 liter
aqueous solution (designated solution R) containing 1099 grams of sodium
bromide. The silver-containing solution utilized was a 1.8 liter aqueous
solution (designated solution A) containing 917.3 grams of silver nitrate
and 1.13 grams of nitric acid. Solutions A and R were added simultaneously
with rapid stirring. The flow of solution R was adjusted so that for the
first two minutes a pAg of 8.36 was maintained, with the next five minutes
allowing for a transition from a pAg of 8.36 to a pAg of 7.16 which was
maintained for the remaining time. A total of 92.5 weight percent of
solution A was added. The remainder of Solution R was set aside for
subsequent use. The resulting product was a cubic silver bromide core
emulsion with a mean grain size of 0.23 micrometers.
Core Sensitization
A 1.5 liter aqueous solution (designated solution L) containing 130 grams
of inert gelatin was added while maintaining the rapidly stirred emulsion
at 40.degree. C. and solution R was added dropwise so as to adjust the pAg
to 8.25. To provide chemical sensitization, 15 mg of sodium thiosulfate
pentahydrate and 12 mg of potassium chloroaurate were added in a
sequential manner and the chemical sensitization reaction was carried out
by raising the temperature to 70.degree. C. for 30 minutes.
Shell Precipitation
The chemically-sensitized core emulsion was shelled by simultaneous
addition of the remainder of solution R and a 1.8 liter aqueous solution
(designated solution B) containing 917.3 grams of silver nitrate with
rapid stirring at 70.degree. C. over a period of 26.8 minutes. The
resulting core-shell emulsion had a mean grain size of 0.290 micrometers.
The core-shell emulsion was washed of excess salts and a 1.5 liter aqueous
solution (designated solution M) containing 200 grams of inert gelatin was
added.
Shell Sensitization
Shell sensitization of the core-shell emulsion was carried out by
sequential addition of 2.8 mg of sodium thiosulfate pentahydrate and 5.6
milligrams of potassium chloroaurate per silver mole. The chemical
sensitization reaction was carried out by raising the temperature to
70.degree. C. for 30 minutes.
A core-shell emulsion, designated Emulsion A' and employed herein as a
control, was prepared in the same manner as control Emulsion A except that
1,8-dihydroxy-3,6-dithiaoctane, a silver halide ripener, was added during
core precipitation in an amount such that the mean grain size of the
core-shell emulsion grains was 0.393 micrometers as compared with 0.290
micrometers for control Emulsion A.
A core-shell emulsion, designated Emulsion A" and employed herein as a
control, was prepared in the same manner as Control Emulsion A except that
1,8-dihydroxy-3,6-dithiaoctane was added during core precipitation in an
amount such that the mean grain size of the core-shell emulsion grains was
0.423 micrometers as compared with 0.290 micrometers for control Emulsion
A.
In the core-shell emulsions made with ripener, the amount of core chemical
sensitization was adjusted downward by multiplying the sulfur and gold
sensitizer values described above by the ratio 0.23/ECD (effective
circular diameter) of the ripened core emulsion. Likewise, the chemical
sensitizer levels for the shell were adjusted downward by multiplying the
values described above by the ratio 0.29/ECD of the ripened emulsion.
A core-shell emulsion, designated emulsion B and having the dopant
hexacyano ruthenium (II) incorporated in the shell, was prepared in the
same manner as emulsion A' except that a 1.45 liter aqueous solution
(designated solution S) containing 14.88 grams of sodium bromide and
0.1084 grams of potassium hexacyano ruthenium (II) was added at a constant
flow rate starting 2.87 minutes after the beginning of shell precipitation
and stopping 4.85 minutes before the completion of shell precipitation.
A core-shell emulsion, designated emulsion B' and having the dopant
hexacyano ruthenium (II) incorporated in the shell was prepared in the
same manner as emulsion A" except that solution S was added at a constant
flow rate starting 2.87 minutes after the beginning of shell precipitation
and stopping 4.85 minutes before the completion of shell precipitation.
A core-shell emulsion, designated emulsion C and having the dopant
hexacyano ruthenium (II) incorporated in the core, was prepared in the
same manner as emulsion A except that a 1.59 liter aqueous solution
(designated solution T) containing 14.88 grams of sodium bromide and 0.119
grams of potassium hexacyano ruthenium (II) was added at a constant flow
rate starting 3.00 minutes after the beginning of core precipitation and
stopping 4.932 minutes before the completion of core precipitation.
A core-shell emulsion designated emulsion C' and having the dopant
hexacyano ruthenium (II) incorporated in the core, was prepared in the
same manner as emulsion A" except that solution T was added at a constant
flow rate starting 3.00 minutes after the beginning of core precipitation
and stopping 4.932 minutes before the completion of core precipitation.
Each of emulsions A, A', A", B, B', C and C' was coated on 7-mil cellulose
acetate support to produce a test film. The melt containing the silver
halide emulsion was coated at 69.9 grams of 40.degree. C. melt per square
meter. Prior to coating, a sensitizing dye, additional inert gelatin and a
nucleator were added to the melt The sensitizing dye employed (designated
dye S-1) was a triethylamine complex of
naphtho(1,2-d)thiazolium-1-(3-sulfopropyl)-2-[(3-sulfopropyl)-2(3H)-benzot
hiazolylidene]methylhydroxide inner salt. The nucleator employed was
nucleator N-A. The pH and pAg values of the melts were 5.6 and 8.0,
respectively. The coverage of inert gelatin in the emulsion layer was 2.69
grams per square meter. A gelatin overcoat hardened with 2.1 weight
percent of the hardener 1,1'-methylenebis(sulfonyl)-bis-ethene was applied
at a gelatin coverage of 0.915 grams per square meter.
The test films were exposed with a Xenon flash sensitometer at 1/14000 of a
second through a filter pack (See David A. Cree, "Sensitometric Simulation
Of The Spectral Emission Of Standard Phosphors", PHOTOGRAPHIC SCIENCE AND
ENGINEERING, Vol. 13, No. 1, p. 18-23, 1969.) that simulates the exposure
from a P22B phosphor of a cathode ray tube employed in typical COM devices
for microfilm. A step tablet with twenty individually calibrated densities
was used to impose an exposure range on the test film strip. The
photographic visual densities of the processed film strips were plotted
versus the log of the known exposure intensities to obtain the
characteristic density versus log exposure curve. From each characteristic
curve, the minimum density, D.sub.min, the maximum density, D.sub.max, and
the toe speed at a point 0.1 density units above D.sub.min was calculated.
The speeds are reported as delta speeds, that is speed increases above
that of the control emulsion.
All of the test films were processed with EASTMAN KODAK MX-1330 developer
at 93.degree. C. in a modified KODAK PROSTAR PROCESSOR that gave 30 second
development time and 30 second fix and wash times.
The emulsion characteristics and photographic parameters are summarized in
Table I below.
TABLE I
__________________________________________________________________________
Nucleator
Mean Grain
Dopant
Location
Concentration Delta
Example Size Level
of (millimoles/ Toe
No. Emulsion
(micrometers)
(PPM)
Dopant
mole Ag)
D.sub.min
D.sub.max
Speed
__________________________________________________________________________
Control 1
A 0.290 0 -- 0.022 0.032
2.26
0
Control 2
A' 0.393 0 -- 0.011 0.082
2.39
0
Control 3
A" 0.423 0 -- 0.011 0.098
2.27
0
Example 1
B 0.391 100 Shell
0.0055 0.039
2.25
22
Example 2
B' 0.424 100 Shell
0.011 0.054
2.20
22
Example 3
C 0.286 60 Core 0.022 0.049
2.20
18
Example 4
C' 0.424 60 Core 0.011 0.066
1.94
29
__________________________________________________________________________
As shown by the data in Table I, incorporation of the dopant hexacyano
ruthenium (II) in either the core or the shell provided a significant
improvement in photographic speed as compared to an undoped emulsion of
similar grain size while also giving comparable D.sub.min and D.sub.max
values. Thus, Example 1 and Control 2 have similar grain sizes but Example
1 exhibits a delta toe speed of 22 due to the presence of the dopant in
the shell. Similar results are seen in comparing Example 2 and Control 3,
in comparing Example 3 and Control 1, and in comparing Example 4 and
Control 3.
EXAMPLES 5-13
Emulsions D, E, F and G, similar to Emulsion C', were prepared except that
the amounts of sulfur and gold sensitizers employed were varied. In each
of emulsions D, E, F and G, the mean grain size was 0.416 micrometers,
hexacyano ruthenium (II) was incorporated in the core in an amount of 60
ppm, and the amount of nucleator N-A was 0.011 millimoles per Ag mole.
Emulsions H, I, J, K and L, similar to Emulsion B, were prepared except
that the amounts of sulfur and gold sensitizers employed were varied. In
each of emulsions H, I, J, K and L, the mean grain size was 0.396
micrometers, hexacyano ruthenium (II) was incorporated in the shell in an
amount of 100 ppm, and the amount of nucleator N-A was 0.022 millimoles
per Ag mole.
The levels of sulfur (sodium thiosulfate pentahydrate) and gold (potassium
chloroaurate) sensitization and the photographic parameters are summarized
in Table II.
TABLE II
__________________________________________________________________________
Weight
Gold Ratio of
Example Sulfur (mg/mole
Gold to Toe
No. Emulsion
(mg/mole Ag)
Ag) Sulfur
D.sub.min
D.sub.max
Speed
Granularity
__________________________________________________________________________
5 D 6.0 2.0 0.33 0.037
2.40
180.2
12.9
6 E 4.0 2.0 0.50 0.040
2.39
181.7
13.3
7 F 2.0 2.0 1 0.037
2.23
189.0
12.6
8 G 2.0 4.0 2 0.057
2.16
192.5
12.4
9 H 4.0 4.0 1 0.08
2.78
233 11.43
10 I 2.0 4.0 2 0.07
2.42
254 11.4
11 J 3.0 6.0 2 0.11
2.49
254 10.18
12 K 2.0 8.0 4 0.12
2.46
247 10.83
13 L 2.0 12.0 6 1.08
2.40
243 11.22
__________________________________________________________________________
As shown by the data in Table II, at a given grain size the weight ratio of
gold sensitizer to sulfur sensitizer affects both speed and granularity.
At an optimum ratio, increased speed and reduced granularity are achieved,
while still maintaining acceptable D.sub.max and D.sub.min values.
EXAMPLES 14-18
Emulsions M, N, O, P and Q, similar to Control Emulsion A were prepared
except that the amount of nucleator N-A was varied. In each of emulsions
M, N, O, P and Q, the mean grain size was 0.290 micrometers, no dopant was
employed, the sulfur sensitizer level was 2.0 mg/mole Ag and the gold
sensitizer level was 4.0 mg/mole Ag.
Emulsions R, S, T, U and V, similar to Emulsion B, were also prepared
except that the amount of nucleator N-A was varied. In each of emulsions
R, S, T, U and V, the mean grain size was 0.396 micrometers, hexacyano
ruthenium (II) was incorporated in the shell in an amount of 100 ppm, the
sulfur sensitizer level was 2.0 mg/mole Ag and the gold sensitizer level
was 4.0 mg/mole Ag.
The concentrations of nucleator employed and the photographic parameters
are summarized in Table III.
TABLE III
______________________________________
Nucleator
Example
Emul- Level Toe Granu-
No. sion (mg/mole Ag)
D.sub.min
D.sub.max
Speed larity
______________________________________
Control 4
M 0.0660 0.21 2.59 186 10.89
Control 5
N 0.0311 0.16 2.21 243 10.26
Control 6
O 0.0220 0.15 2.16 259 11.96
Control 7
P 0.0156 0.14 1.99 260 9.05
Control 8
Q 0.0110 0.12 1.04 266 14.91
14 R 0.0440 0.12 2.45 236 10.93
15 S 0.0220 0.07 2.42 254 11.40
16 T 0.0110 0.06 2.50 260 10.85
17 U 0.0078 0.05 2.51 258 11.02
18 V 0.0055 0.04 2.40 260 12.09
______________________________________
As shown by the data in Table III, the photographic speed and D.sub.max of
the undoped control emulsions varied much more drastically with change in
nucleator level than did the photographic speed and D.sub.max of the doped
emulsions prepared in accordance with this invention. Thus, exact control
of nucleator concentration is much less critical with the doped emulsions.
EXAMPLES 19-25
Emulsions (a), (b), (c), (d), (e), (f) and (g), similar to emulsion B, were
prepared to compare the performance of nucleator N-A with the performance
of nucleator N-B. In each of emulsions (a), (b), (c), (d), (e), (f) and
(g), the mean grain size was 0.424 micrometers, hexacyano ruthenium (II)
was incorporated in the shell in an amount of 100 ppm, the sulfur
sensitizer level was 2.0 mg/mole Ag and the gold sensitizer level was 4.0
mg/mole Ag.
The concentrations of nucleator employed and the photographic parameters
are summarized in Table IV.
TABLE IV
__________________________________________________________________________
Nucleator
Example Nucleator
Level Toe
No. Emulsion
Employed
(mg/Ag mole)
D.sub.min
D.sub.max
Speed
Granularity
__________________________________________________________________________
19 (a) N-B 0.022 0.395
1.83
105 13.68
20 (b) N-B 0.011 0.289
1.69
127 13.46
21 (c) N-B 0.0055 0.167
1.51
175.6
--
22 (d) N-B 0.0022 0.081
1.62
200 13.50
23 (e) N-B 0.0011 0.050
1.74
196.4
14.18
24 (f) N-B 0.00055
0.032
l.77
199.2
15.08
25 (g) N-A 0.011 0.063
2.02
193.3
13.85
__________________________________________________________________________
As shown by the data in Table IV, nucleator N-A provides a significantly
better D.sub.max at comparable speed than does nucleator N-B.
Considering the data in all of the examples above, it is apparent that
hexacyano ruthenium (II) is a remarkably effective doping agent for
direct-positive core-shell emulsions. It provides excellent photographic
speed while permitting the use of silver halide grains of sufficiently
small size that the developed granularity level is fully acceptable for
COM applications. It also gives fully acceptable values for D.sub.min and
D.sub.max.
The invention has been described in detail, with particular reference to
certain preferred embodiments thereof, but it should be understood that
variations and modifications can be effected within the spirit and scope
of the invention.
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